Field of the Invention
A sheet feeder system of a sheet-fed printing press has a function of individually separating sheets which have been precisely prepiled on a sheet support board and of supplying them in succession to a feeder of the printing press. Mainly two sheet feeder systems for sheet-fed offset printing presses are known in the present state of the art, namely a system having a single-sheet feeder with a sucker bar, and a system having a shingle or stream feeder with a suction head.
In the case of a single-sheet feeder, the uppermost sheet of a sheet pile is pneumatically lifted at the leading edge thereof by a plurality of suckers fastened to a bar, and then taken over by feed grippers or transport rollers. The feed grippers or transport rollers guide each sheet individually to the feeder of the printing press. By adjusting the suction force, by changing the tilt of the suction bar and by the action of blast air blown against the leading edge of the pile, the single-sheet feeder may be adapted to different thicknesses of paper and different paper qualities. The instant the separated sheet has run into the printing press, a new sheet may be individually separated. Consequently, in the case of a single-sheet feeder, the sheets have to be separated individually very quickly in order to attain the intended press speed.
For higher press speeds, shingle or stream feeders are used wherein the sheets are singled out or individually separated at the trailing edge of the pile by a suction head. A stream-feeder has various pneumatic separating and forwarding or pull suckers which remove the uppermost sheet and continuously feed it to a feeding table. In addition, various blowing devices, stripping or separating brushes, stripping or separating plates and sheet retainers or down-holders are disposed at the trailing edge of the feeder in order to ensure a trouble-free separation and to provide for a smooth and straight transport of the sheets which are disposed in an overlapping or shingled manner on the feeding table. During a brief stop at the feeder, each sheet is aligned so as to be in register. The pressman must precisely adjust the blast air and the suction air, as well as the aforementioned auxiliary equipment, to the respective printing material which is being used.
In conventional feeder systems, suction air and blast air, respectively, are required, and the higher the operating speed, the greater the number and the greater the efficiency of the suction devices and blowing devices are necessary, for a correspondingly high air consumption. The suction devices and blowing devices cause considerable noise, and the periodic switching-on and switching-off of the air flows and the motion of the suction heads in accordance with the press cycle result in the production of vibrations which are difficult to cope with.